Strollers have become standard equipment in every family raising children. The usual ones have a single seat mounted on some sort of structure provided with four small wheels. The front pair of wheels are usually casters, and a jointed tongue extends from the castered end to a handle that permits the stroller to be pulled along behind as a person walks. Pushed versions are also common. These devices can be used from the time the infant can sit up until he can walk well enough on his own to keep up with the adult.
Cost is a significant factor in the purchase of strollers, and this is particularly true when a family may have several "passengers", or where child-care centers may have a group of children to transport at the same time. A separate stroller for each is often prohibitive. Often, the stroller will be broken before it is worn out, complicating the cost problem.